Apparatus for transporting or pumping materials are well known in the art. Conventional gear pumps are typically constructed in a manner as shown in FIG. 1. Such pumps include a pump body 1 having an inlet and outlet end (not shown), a pair of herringbone gears 2 & 3, a pair of side plates 4 & 5, two internal double roller bearings 6 mounted on each of the side plates 4 & 5 (FIG. 2) and two gear support shafts 7 & 8 mounted for rotation in bearings 6. These pumps are particularly well suited for pumping, for example crude oils, and other materials having a viscosity up to about 1.0.times.10.sup.5 centipoise (cps).
An earlier pump for materials having a viscosity up to about 1.0.times.10.sup.5 cps is disclosed and illustrated in U.S. Pat. No. 4,859,161. The pump uses double roller bearings mounted on rotational side plates which enables the rotation of the pump to vary without changing the structure of the pump. Other pumps that use some sort of gear arrangement are disclosed in U.S. Pat. Nos. 4,329,128 and 4,806,080. In each of these prior art pumps, only low viscosity materials can be pumped because there are no means of reducing the pressure buildup in the pump housing, and particularly, reducing the load on the shaft and bearing assembly. Thus, severe premature pump and/or component part wear would result if these pumps were used to transport materials having viscosities very much greater than 1.0.times.10.sup.5 cps.
Accordingly, a major shortcoming of earlier pumps is that they are not adapted for transporting materials having viscosities greater than about 1.0.times. 10.sup.5 cps. Much beyond this viscosity, the integrity of the pump components is severely compromised. The life of gear pump bearings, for example, depends primarily on the load on the bearing and shaft assembly, discharge pressure, liquid viscosity, and proper alignment of the components like shafts and bushings and, to a lesser extent, on the speed and operating temperature. Thus, in order to transport highly viscous materials, e.g., cellulose acetate with a viscosity of about 3.0.times.10.sup.5 cps, it is crucial that the wear rates of the bearings and associated components of the apparatus are minimized. Moreover, the excessive wear of the conventional double roller bearings used in conventional pumps leads to the wear and misalignment of the gear assembly and wear of the side plates that support the bearings. These component compromises, particularly at high shaft/bearing assembly loads caused by pumping high viscosity materials, result in an eventual catastrophic failure of the conventional pump.
Therefore, a need exists for a pump to transport highly viscous materials, such as cellulose acetate, which will not be subject to the high wear rates and severe failures of conventional pumps.